In a low pressure die casting apparatus, molten metal is forced upwardly through a riser tube having its lower end extending below the level of molten metal in the bath or crucible of a furnace and having an apertured cap at its upper end which is connected to the inlet of the die. The molten metal is raised by applying gas pressure to the surface of the molten metal in the furnace; the molten metal rising up the riser tube and into the die where the metal solidifies. The gas pressure is then reduced allowing excess molten metal to fall back down the riser tube to the bath or crucible in the furnace after which the die is opened to remove the casting therefrom.
As the level of the molten metal in the furnace changes due to consumption of the metal or to refilling of the bath, the pressure conditions in the apparatus change. The principal factors influencing these pressure changes are the changing volume of air in the furnace and the changing "head" pressure required to lift the molten metal to the die as the level in the furnace changes.
The invention aims at providing automatic compensation for changes in the level of the molten metal in low pressure die casting apparatus without the complexity and expense of installing level floats or magnetic or nuclear sensing devices for indicating the level of the metal.